(1) Field of the Invention
The present invention relates to a technique for creating an entry map.
(2) Description of the Related Art
An entry map is information used for reading data at a certain location in a data stream, where decoding can be started. For instance, an entry map for a video indicates the address and the size of each I-picture (Intra picture). A technique for creating such an entry map is necessary for playing back a video stream that is encoded with use of correlativity among frames, such as in MPEG-2 and MPEG-4 AVC, and this technique is adopted in BD-RE standard.
If the video stream is encoded by an encoding method such as MPEG2-Video and MPEG4-AVC, it is compressed with use of correlativity among frames included in the stream, and accordingly the P-picture and the B-picture can not be decoded unless the I-picture is decoded in advance. Therefore, a playback device reads an entry map, and interprets where to start reading the data. The entry map enables the playback device to immediately judge where, in the video stream, to start reading in order to decode the I-picture firstly, without actually analyzing the content of the stream. Using the entry map, it becomes possible to read I-pictures continuously without reading redundant data. This realizes special playback operations such as a playback at high speed and a reverse playback in a suitable manner, even if the video stream is recorded on a low-speed recording medium, such as an optical disc.
The following describes the entry map. The entry map includes entries, which are pieces of information about I-pictures included in the video stream. Each entry includes a pair of an I_start and an I_end.
The I_start is a relative address relative to the beginning of the video stream. The I_end is a 3-bit value showing the size of the I-picture. The size of the I-picture is represented by only 3-bit wide data, because a lot of I-pictures are included in the video stream and it is demanded that data for each I-picture should be represented in a short form.